The present invention relates generally to electrical assemblies that include two or more interconnected circuit boards, and more particularly, to electronic assemblies for flat panel displays, and methods of their manufacture.
For various applications, it is necessary to electrically and mechanically connect circuit boards. In some cases, the circuit boards are composed of different substrate materials, such as glass, ceramic, organic materials or other materials. For example, some types of flat panel displays include electronic sub-assemblies, each of which includes a ceramic circuit board electrically connected to a glass plate. The glass plate holds an array of organic light emitting diode (OLED) pixels, which are driven by circuitry on the ceramic circuit board. While manufacturing such an assembly, it is necessary to simultaneously establish hundreds or thousands of electrical interconnections between the circuit board and the OLED pixels on the glass plate.
Some prior art methods of electrically connecting circuit boards use a reflow process. Using this process, solder is selectively deposited on either or both of the circuit boards"" bond pads, the circuit boards are aligned and pressed together, and the assembly is heated until the solder melts and reflows. Unfortunately, several factors make this method of simultaneously forming a large number of electrical interconnections prone to low manufacturing yields. In particular, variations in circuit board flatness, pad coordinates, alignment, and lamination pressure may result in open circuits between some complementary bond pads. This is particularly true when the interconnections are spread over relatively large areas on the surfaces of the circuit boards.
What are needed are interconnected circuit board assemblies that are less prone to open circuit defects due to variations in circuit board flatness, pad coordinates, alignment, and lamination pressure. Further needed are high yield methods of manufacturing interconnected circuit board assemblies.